Mitered core construction



March 2, 1965 T. H. KEoGH ETAL 3,172,066

MITERED CORE CONSTRUCTION Filed Oct. 6, 1959 United States Patent O 73,172,666 MEERED CRE CNSTRUCTiGN Thomas H. Keogh and Hans Il. Weber,Pittsburgh, Pa., assigner-s to Allis-Chalmers Manufacturing Company,Miiwaukee, Wis.

Filed Oct. 6, 1959, Ser. No. 844,772 6 Claims. (Cl. 336-217) Thisinvention relates to electric induction apparatus and more particularlyto a laminated core structure for a three phase transformer.

At one time, the layers of three phase stacked laminated transformercores comprised three leg pieces and four yoke pieces, all of which wererectangular. r`hus, all of the leg pieces were identical and likewisethe yoke pieces were identical. As development continued, it wasdiscovered that certain grades of magnetic sheet material which had beenhot rolled have a higher degree of permeability in the direction ofrolling as compared to other directions. lt was also learned that lossesare least when the flux lines are parallel to the direction of rollinginstead of across the grain. In order to take full ad- Vantage of steelhaving a preferred magnetic direction, leg and yoke pieces have beenmade with diagonal or mitered ends. The resulting mitered butt jointspermit the lines of flux to form in the direction of least magnetizationthroughout the core layers. t was further learned that by staggering oroverlapping the mitered butt joints of adjacent layers to avoidcoincident joints, separation of the laminations is minimized.

As the above developments occurred, it was only natural that theindividual pieces comprising a core became more complex in theirconiiguration. The number of ditierent congurated pieces in each layeralso increased with as many as four different pieces comprising onelayer of a three phase core. Thus, while transformers became more andmore ellicient, the cost of making the various pieces for the core alsoincreased.

The three phase core of this invention uses pieces of only two dierentconfigurations which are relatively simple in des-ign and yet still forman advantageous butt lapped mitered joint structure. The three legpieces in each layer of the core are identical in configuration, as arethe four yoke pieces. With the need for only two different contiguratedpieces in a layer, stock piling becomes relatively simple since only twopiles are required. Set up time is also reduced. By providing the endportions of the leg pieces with tapered ends, the outside right anglecorners normally present in an assembled core are eliminated andconsequently a lighter core is provided.

Thus, it is one object of this invention to provide a new and improvedthree phase laminated core having butt lapped mitered joints,

Another object of this invention is to provide a new and improved threephase core having reduced weight.

Another object of this invention is to provide a new and improved threephase core in which each layer comprises pieces having only twodifferent shapes.

Another object of this invention is to provide a new and improvedlaminated core having efficient magnetic characteristics which may bemanufactured at a reduced cost.

Further objects and advantages of the present invention will be apparentfrom the description and accompanying drawings, and will be moreparticularly pointed out in the claims.

In the accompanying drawing:

FIG. l illustrates an arrangement of stacked layers of magnetic sheetmaterial arranged in accordance with this invention;

FIG. 2 illustrates a modification of this invention.

3,17%@66 Patented Mar. 2, 1965 ICC The structure shown in FIG. lillustrates a three phase core 1o having but lapped mitered core jointsin accordance with this invention. Legs 11 and yokes 12 of the core areident-ical in width and are formed from strip material which has higherpermeability in the lengthwise direction which is the direction ofrolling. The three leg pieces 11 are identical in configuration. The legand yoke pieces have all been cut with their lengths parallel to themost favorable magnetic direction in order to obtain a highly eiiicienttransformer. Each leg has two extending end portions 14 with each of theend portions being outlined by two edges 1o and 17 which converge toform acute angles A. The angle edges 16 and 17 are preferably positionedin such a manner that a line bisecting the angle A therebetween isparallel to the longitudinal center line 13 of the leg. In the preferredembodiment, apex 19 of each angle A forming the end portions is on aline offset or askew with longitudinal center line 18, The end 19 ofeach of the end portions also terminates within the area bordered by anextension of the lines forming the longitudinal edges of the leg piece.Each yoke piece 12 is in the shape of an isosceles trapezoid lwhich addsto the simplicity of assembly. lf the bisecting line of the angle A isnot parallel to the longitudinal center line, then the yoke is atrapezoid in which the non-parallel edges are unequal in length.

Overlapping of core joint 21 is achieved by providing each leg piecewith a pointed end. The point 19 of each end is preferably otiset fromthe center line 1S. In this manner, each layer in the core can have itsjoint edges offset from the joint edges in adjacent layers, atfording anoverlapping effect on the joints. In assembling the core, the leg piecesin one layer are arranged inversely congruent to the superposed legpieces in adjacent layers. Since the leg pieces are unsymmetrieal withrespect to their longitudinal center line 18, it is relatively easy toarrange the layers to obtain butt lapped joints. The leg pieces l11 inalternate layers are identically positioned while the leg pieces in theadjacent layers may either have their ends 19 reversed or be turned overto stagger the edges 16 and 17. In such a manner, the assembly of threephase cores is relatively easy. There need be only two stock piles ofcore pieces and consequently there is considerable ease in assemblingthe two pieces to form a three phase core. The fact that the core ofthis invention does not have rectangular corners which have heretoforeappeared in three phase transformers of the prior art is not a limitingone. The lack of rectangular corners does not cause any excessive lossesas the core cross section taken perpendicular to the flux remainsubstantially as large in the corners as in the remainder of the core.The weight of the core is thereby reduced without affecting theperformance characteristics of the transformer.

The preferred embodiment illustrated in FIG. l has leg pieces having anend portion 14 with an angle A of 53 10. Angle B between a joint edge 21and edge 22 of yoke 12 is 63-25. While the angle A of the end portion ofthe leg pieces could be less, it is believed that the angle ofapproximately 53 will provide the best pattern for providing the leastflux resistance. When the end angle A is less than 53 one of the miteredjunction lines delining end portion 14 will approach a perpendicularposition with respect to the adjoining yoke 12 and consequently theresulting structure is less eflicient.

FIG. 2 illustrates a second embodiment of the invention. Leg pieces 26have two edges 27 and 2S which are equal in length. The result is thatthe overlap between junction line 31 in one layer and junction line 32in an adjacent layer is tapered with the overlap being widest at theouter perimeter of the core. The advantage in this, which has previouslybeen recognized, is that the joint reluctance at the outer perimeter isreduced `thereby oisetting the greater reluctance which normally occursat the longer perimeter. In such a manner, the total reluctance is moreuniform and the flux lines are more equally distributed. Heretofore,three phase cores having this feature required four dilerent dies tostamp out the pieces comprising each layer. The structure in theembodiment of FIG. 2 retains the advantages of the prior art whilerequiring only two dies.

Although but two embodiments have been shown and described, it will beapparent to those skilled in the art that various changes andmodiications may be made therein without departing from the spirit ofthe invention or the scope of the appended claims.

Having now particularly described and ascertained the nature of our saidinvention andt he manner in which it is to be performed, we declare thatwhat we claim is:

1. A magnetic core for three phase electrical apparatus comprising: aplurality of layers of magnetic sheet material, each said layer havingthree leg pieces of like coniguration and four yoke pieces of likeconfiguration connecting said leg pieces to form two substantiallyrectangular windows, said leg and yoke pieces having the same width,each said leg having two extending end portions, each said end portionformed by two edges converging in directions acute with the longitudinalcenter line of said leg, the apex of the angle formed by the edges ofone of said end portions being oilset from said center line, each saidyoke piece defining a trapezoid, and each saidrlayer having its piecesinversely congruent to said superposed pieces in said adjacent layerswhereby the superposed joint edges in said adjacent layers provide anoverlap.

2. A magnetic core for three phase electrical apparatus comprising: aplurality of similar layers of magnetic sheet material, each said layerhaving three leg pieces ot like configuration and four yoke pieces oflike configuration connecting said leg pieces to form a substantiallyrectangular core, said leg and yoke pieces being of the same width andhaving their lengths parallel to the most favorable magnetic directionof said material, each said leg piece having each end deiined by jointedges terminating at a point within the area bordered by an extension ofthe lines forming the longitudinal edges of said leg piece with at leastone of said end points being offset from the longitudinal center line ofsaid leg piece, each said yoke piece forming an isosceles trapezoid, andeach said layer having its pieces inversely congruent to said pieces inadjacent layers whereby said joint edges in a layer are overlapped bysaid pieces in said adjacent layers.

3. A magnetic core for three phase electrical apparatus comprising: aplurality of similar layers of magnetic sheet material, each said layerhaving three leg pieces of like configuration and four yoke pieces oflike conguration connecting said leg pieces to form two substantiallyrectangular windows, said leg and yoke pieces being of the same widthand having their lengths parallel to the most favorable magneticdirection of said material, each said leg piece having each end definedby joint edges terminating at a point within the area bordered by an eX-tension of the lines `forming the longitudinal edges of said leg piecewith at least one of said end points before offset from the longitudinalcenter line of said leg piece, each said yoke piece forming a trapezoid,and each said layer having its leg pieces inversely congruent to saidleg pieces in adjacent layers whereby said joint edges in a layer areoverlapped by said pieces in adjacent layers.

4. A magnetic core for three phase electrical apparatus comprising: aplurality of layers of magnetic sheet material, each said layer havingthree leg pieces of like configuration and four yoke pieces of likeconiguration connecting said leg pieces to form two substantiallyrectangular windows, said leg and yoke pieces have the same width withtheir lengths parallel to the most favorable magnetic direction of saidmaterial, each said leg having two extending end portions, each said endportion formed by two edges defining an acute angle whereby a linebisecting said angle is parallel and offset from the longitudinal centerline of said leg, each said yoke piece defining an isosceles trapezoid,and each said layer having its pieces inversely congruent to saidsuperposed pieces in said adjacent layers whereby said joint edges in alayer are overlapped by said pieces in said adjacent layers.

5. A magnetic core for three phase electrical apparatus comprising: aplurality of similar layers of magnetic sheet material, each said layerhaving three leg pieces of like configuration and four yoke pieces oflike configuration connecting said leg pieces to form two substantiallyrectangular windows, said leg and yoke pieces being of the same widthand having their lengths parallel to the most favorable magneticdirection of said material, each said leg piece having each end definedby joint edges terminating at a point within the area bordered by anextension oli the lines forming the longitudinal edges of sa-id legpiece with at least one of said end points being oiset from thelongitudinal center line of said leg pierce, each said yoke pieceforming a trapezoid, and each said layer having its leg pieces inverselycongruent to said leg pieces in adjacent layers whereby said joint edgesin a layer are overlapped by said pieces in adjacent layers and parallelto the respective joint edges in adjacent layers.

6. A magnetic core for three phase electrical apparatus comprising: aplurality of similar layers of magnetic sheet material, each said layerhaving three leg pieces of like coniguration and four yoke pieoes oflike conguration connecting said leg pieces to form two substantiallyrectangular windows, said leg and yoke pieces having their lengthsparallel to the most favorable magnetic direction of said material, eachsaid leg piece having each end defined by joint edges terminating at apoint within the area bordered by an extension of the lines forming thelongitudinal edges of said leg piece with at least one of said endpoints being offset from the longitudinal center line of said leg piece,each said yoke piece forming an isosceles trapezoid, and each said layerhaving its leg pieces inversely congruent to said leg pieces in adjacentlayers whereby said joint edges in a layer are overlapped by said piecesin adjacent layers and parallel to the respective joint edges inadjacent layers.

References Cited in the tile of this patent UNITED STATES PATENTS

1. A MAGNETIC CORE FOR THREE PHASE ELECTRICAL APPARATUS COMPRISING: APLURALITY OF LAYERS OF MAGNETIC SHEET MATERIAL, EACH SAID LAYER HAVINGTHREE LEG PIECES OF LIKE CONFIGURATION AND FOUR YOKE PIECES OF LIKECONFIGURATION CONNECTING SAID LEG PIECES TO FORM TWO SUBSTANTIALYRECTANGULAR WINDOWS, SAID LEG AND YOKE PIECES HAVING THE SAME WIDTH,EACH SAID LEG HAVING TWO EXTENDING END PORTIONS, EACH SAID END PORTIONFORMED BY TWO EDGES CONVERGING IN DIRECTIONS ACUTE WITH THE LONGITUDINALCENTER LINE OF SAID LEG, THE APEX OF THE ANGLE FORMED BY THE EDGES OFONE OF SAID END PORTIONS BEING OFFSET FROM SAID CENTER LINE, EACH SAIDYOKE PIECE DEFINING A TRAPEZOID, AND EACH SAID LAYER HAVING ITS PIECESINVERSELY CONGRUENT TO SAID SUPERPOSED PIECES IN SAID ADJACENT LAYERSWHEREBY THE SUPERPOSED JOINT EDGES IN SAID ADJACENT LAYERS PROVIDE ANOVERLAP.